The present invention relates to a printed matter including invisible information that is generated by printing an invisible information pattern on the base pattern of the printed matter and that can be visualized for visual identification by putting a reference pattern, corresponding to the base pattern, on the printed matter.
Recently, as more data has become digitized and more digital information has become accepted, various technologies for digital signatures and digital watermarks are being studied. These technologies allow copyright information or other attribute information to be added to digital information as invisible information. A method, called a techniques for embedding secret information, is used as an implementation of these technologies. This technology, used to embed additional information into main image information as invisible information, is useful in preventing copyrighted image data such as pictures, bills, and notes from being copied or altered.
For example, JP-A-11-168616 discloses a method for implementing this technology. In this method, image information to be embedded is created from additional information composed of characters and images and, from the image information to be embedded, combined image information is created by modulating the predetermined pattern image information. The combined image information is then recorded on a non-electronic medium such as a paper.
Another method is described in xe2x80x9cBasics of Digital Watermarksxe2x80x9d, by Kineo Matsui, pp. 22-26, 1998, Morikita Publishing Co. This method converts the shade of an image to micro-pattern density information to represent monochrome gray scale picture information and so on. It overlaps one micro-pattern on another to make watermark information visible. For example, in a part where information in a predetermined shape such as character information is present, the method inverts monochrome information for reproducing intermediate colors between white and black and prints it as invisible information on a medium such as a paper. On the other hand, the monochrome information, which is not inverted, is printed on a non-electronic medium such as a transparent film. Then, this method physically puts the transparent film on the paper to cause invisible information part, such as the shade of the character area, to be distinguished from other parts to allow invisible information to be made visible.
JP-A-6-40190 discloses an ID card that prevents counterfeiting. A transparent film with special thin lines or a net pattern, or a lenticular film with a special frequency, is put this ID card. This structure causes at least two sets of thin-line or net patterns, each generating its own moirxc3xa9, to appear in different areas.
To extract invisible information from a non-electronic medium, such as a paper, using the method disclosed in JP-A-11-168616, a mask sheet with the size and the resolution equal to those of the combined image information must be put physically on the combined image information. By doing so, the invisible information is visualized and decoded and the embedded information is reproduced. However, this requires the user to position mask sheet precisely on the combined image information. For precise positioning, the method disclosed in the above-mentioned publication requests that positioning marks be recorded on combined image information. However, putting a mask sheet precisely on combined image information requires the user to use a special positioning apparatus or to manually position the mask sheet on the combined image information carefully and slowly. This work is not easy to do.
The method described in xe2x80x9cBasics of Digital Watermarksxe2x80x9d, by Kineo Matsui, pp. 22-26, 1998, Morikita Publishing Co. also requires the user to put a mask sheet on combined image information precisely to a precision of a macro-pattern cell to visualize embedded information. Thus, visualizing embedded invisible information requires the user to use a special positioning apparatus or to manually position the mask sheet on the composite image information carefully and slowly. This work is not easy to do.
The counterfeit-prevention ID card disclosed in JP-A-6-40190 has at least two sets of different thin line or net patterns. Their frequencies are made to vary to such an extent that human beings cannot detect, or the patterns are placed such that they are not virtually parallel. Means is disclosed for visually checking the validity of the card by putting a film (identification film) with a predetermined frequency on the card to generate a unique moirxc3xa9 for comparing the relative relation. With at least two different patterns arranged separately, this means compares a moirxc3xa9, generated by putting the identification film on the card, with a moirxc3xa9, generated by putting the identification film on the real card, to validate the card. However, means for obtaining invisible information from a thin line pattern or a net pattern is not disclosed. Neither is disclosed a method for making the boundary between at least two separate thin line or net patterns difficult to identify.
It is therefore an object of the present invention to provide a printed matter in which additional information may be invisibly embedded in a base pattern forming the ground pattern and which allows the invisible information to be made visible by putting on the base pattern an identification film or a reference pattern printed on a transparent film.
To solve the problems described above, a printed matter according to the present invention comprises a base pattern formed of stripes at a predetermined interval; and an additional information pattern having information to be added to the base pattern, the information being a pattern of stripes at the predetermined interval of the base pattern, wherein a boundary between the base pattern and the additional information pattern has a predetermined dislocation between the striped pattern of the base pattern and the striped pattern of the additional information pattern and wherein the boundary is at an angle equal to or larger than a predetermined angle.
In addition, the printed matter according to the present invention is a printed matter printed with a digital printer, and an amount of the dislocation in the boundary between the base pattern and the additional information pattern is a minimum unit of resolution of the digital printer.
Still further advantages of the present invention will become apparent to those of ordinarily skill in the art upon reading and understanding the following detailed description of the preferred and alternate embodiments.